8–2
Chapter 8: External Memory Interfaces in the Cyclone III Device Family
Cyclone III Device Family Memory Interfaces Pin Support
shows the block diagram of a typical external memory interface data path
in Cyclone III device family.
Figure 8–1. Cyclone III Device Family External Memory Data Path
DQS/CQ/CQn
DQ
OE
IOE
Register
OE
IOE
Register
IOE
Register
VCC
IOE
Register
IOE
Register
DataA
IOE
Register
LE
Register
GND
IOE
Register
DataB
IOE
Register
LE
Register
LE
Register
System Clock
PLL
-90° Shifted Clock
Capture Clock
Note to
(1) All clocks shown here are global clocks.
Cyclone III Device Family Memory Interfaces Pin Support
Cyclone III device family uses data (DQ), data strobe (DQS), clock, command, and
address pins to interface with external memory. Some memory interfaces use the data
mask (DM) or byte write select (BWS#) pins to enable data masking. This section
describes how Cyclone III device family supports all these different pins.
Data and Data Clock/Strobe Pins
Cyclone III device family data pins for external memory interfaces are called D for
write data, Q for read data, or
DQ
for shared read and write data pins. The read-data
strobes or read clocks are called
DQS
pins. Cyclone III device family supports both
bidirectional data strobes and unidirectional read clocks. Depending on the external
memory standard, the
DQ
and
DQS
are bidirectional signals (in DDR2 and
DDR SDRAM) or unidirectional signals (in QDR II SRAM). Connect the bidirectional
DQ
data signals to the same Cyclone III device family
DQ
pins. For unidirectional
D
or
Q
signals, connect the read-data signals to a group of
DQ
pins and the write-data signals
to a different group of
DQ
pins.
1
In QDR II SRAM, the Q read-data group must be placed at a different V
REF
bank
location from the D write-data group, command, or address pins.
In Cyclone III device family,
DQS
is used only during write mode in DDR2 and
DDR SDRAM interfaces. Cyclone III device family ignores
DQS
as the read-data strobe
because the PHY internally generates the read capture clock for read mode. However,
you must connect the
DQS
pin to the
DQS
signal in DDR2 and DDR SDRAM interfaces,
or to the
CQ
signal in QDR II SRAM interfaces.
Cyclone III Device Handbook
Volume 1
July 2012 Altera Corporation
ALTERA [ ALTERA CORPORATION ]
